Triiodothyronine

The thyroid gland secretes the thyroid hormones triiodothyronine (T3) and thyroxine (T4) into the bloodstream. These hormones are essential for controlling the body's metabolic rate, as well as for growth, bone metabolism, cardiovascular health, and the normal development of the nervous system and gonadal organs. T3 is circulating in the bloodstream as a balanced combination of hormones that are free and attached to serum. The unbound, physiologically active version of T3 is called free T3 (fT3). One benefit of measuring free T3 is that it remains unaffected by variations in the quantities and characteristics of the proteins that bind. In clinical routine diagnostics, free T3 is a helpful tool for determining the thyroid health. Free T3 measures are essential for the differential diagnosis of thyroid problems, the identification of patients with T3 thyrotoxicosis, and the differentiation of various kinds of hyperthyroidism.